intro_gui

INTRODUCTION TO THE
GRAPHICAL USER
INTERFACE (GUI) IN MATLAB

Video of the Week
 https://www.youtube.com/watch?v=wSnx4V_R
ewE

What is a GUI?
 Graphical User Interface
 What?
 A pictorial based interface that uses menus, buttons,
the mouse, and other “graphics” to communicate with
the user. [No command line interaction]
 Examples:
 The Windows Calculator
 Firefox, Thunderbird, Office
 Anything you are looking at [on the computer].

What is a GUI in MATLAB?
 GUI’s in MATLAB consist of two files:
 An “m-file” [******.m]
 A “fig-file” [******.fig]
 The m-file has all of the code that controls the
GUI
 The fig-file has all of the graphical objects,
positions, default values, and links it all together

MATLAB GUI -- Example
Edit Text
Boxes
Radio
Button
Push Button
Axes
Panel
Static Text
Pop Up-menu

MATLAB GUI -- Example
Sliders
to Change figure.
This is the “Superquadrics”
demo included with MATLAB.

Handle Graphics
 Handle graphics are low-level graphic
functions that control characteristics generated
by MATLAB. They allow the programmer to
have precise control of the appearance of plots
and graphics.1
 Examples: turning the grid on or off, changing
colors or line types of plotted data, changing the
marker type or line width.
1 Chapman, Stephen J. MATLAB Programming for Engineers. 2005

Handle Graphics
 Each component has a list of properties that
define what it looks like and how it behaves.
 Plot Something:
 Figure Window  View  Property Editor
 More Properties

Handle Graphics
 The manipulation of these properties form the
basis of GUIs and GUI programming in
MATLAB.
 The ‘handle’
 >> fh = figure();
>> set(fh,'Name','Figure: Meet the World!');
>> set(fh,'NumberTitle','off');
>> ph = plot([1:10],[1:10].^2);
>> set(ph,'LineStyle','--');
>> set(ph,'Marker','square');
>> set(ph,'MarkerEdgeColor',[1 0 0],
'MarkerFaceColor',[0 1 0]);
>> get(ph); get(fh); %Look at all properties

Handle Graphics
 The ‘set’ and ‘get’ commands
 These are the primary commands that you use to
… set and get information about graphic objects,
they update the graphical object immediately
 Syntax: ‘set’
>> set(object_hndl,'PropertyName',propvalue);
 Syntax: ‘get’
>> propvalue = get(object_hndl,'PropertyName');

Creating a GUI
 Step 1: Create the graphical components
 Using the GUIDE
 Manually configure each component
 Step 2: Program components
 The GUIDE will generate the primary file, you
must add to this file all of the actions your
components will take.
 Step 3: Interface with your analysis tools
 We are working on a way for the user to work with
your code in an efficient manner.

Step 1:The GUI – The Guide
Type ‘guide’ into the command window or:

Step 1: The GUI – The Guide
 Step 1(cont.): Create a new GUI

Tool Use
Layout Editor Select components from the component palette, at the left side of
the Layout Editor, and arrange them in the layout area.
Figure Resize Tab Set the size at which the GUI is initially displayed when you run it.
Menu Editor Create menus and context, i.e., pop-up, menus.
Align Objects Align and distribute groups of components.
Tab Order Editor Set the tab and stacking order of the components in your layout.
Property Inspector Set the properties of the components in your layout. It provides a
list of all the properties you can set and displays their current
values.
Object Browser Display a hierarchical list of the objects in the GUI.
Run Save and run the current GUI.
M-File Editor Display, in your default editor, the M-file associated with the GUI.

 MATLAB’s help files are going to help you the
most.
 Search for:
 GUIDE: Tools Summary
 Previous two slides plus more details on each part
 Creating a GUI with GUIDE
 Step by step how to create a simple GUI

Step 1: Creating the GUI - [fig
file]
 Place Components
 Figure out what you want.
 Inputs
 Outputs
 Parameters / Configuration Options?
 Choose appropriate components
 See List
 Place the objects
 Click on icon [from component palette]
 Click and drag in Layout Area
 Configure the component
 Double Click on component or right click and click on Property Inspector.
 Change attributes
 Align components

Step 1: Complete
 We have placed our components and now:
 Press save
 Name your file
 Up pops an m-file
 Notice there is a lot of code
 There is even more pseudocode
[This is a good thing]
 Let’s take a closer look

Step 2: Creating the GUI – [m
file]
 Programming the GUI
 GUI Files: An Overview
 GUI M-File Structure
 Callbacks: An Overview
 Callback Input Arguments
 Adding Callbacks to GUI M-File
 Useful Commands
 Examples of GUI Components

Step 2: Programming the GUI
Section Description
Comments Displayed at the command line in response to the help
command. Edit these as necessary for your GUI.
Initialization GUIDE initialization tasks. Do not edit this code.
Opening
function
Performs your initialization tasks before the user has access
to the GUI.
Output
function
Returns outputs to the MATLAB command line after the
opening function returns control and before control returns to
the command line.
Component
and figure
callbacks
Control the behavior of the GUI figure and of individual
components. MATLAB calls a callback in response to a
particular event for a component or for the figure itself.

 Callbacks: An Overview
 What is a Callback
 A function associated with a GUI component. It
controls the behavior by performing an action in
response to an event.
 Kinds of Callbacks
 Table

 Callback Syntax and Arguments
 Most callbacks will look similar to this:
% --- Executes on button press in pushbutton1.
function pushbutton1_Callback(hObject, eventdata, handles)
% hObject handle to pushbutton1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
...
 Insert your code after the last comment
 Read the comments, they might help you

 Naming of Callbacks
 function pushbutton1_Callback(hObject, eventdata, handles)
name
 Input Arguments
 hObject  Handle of the object, e.g., the component
 eventdata  Reserved for later use.
 handles  Structure that contains the handles of all the objects in the
figure. It may also contain application-defined data.

 Adding Callbacks
 The GUIDE only creates the most common
callbacks
 You may want to create different ones:
 Right-click on the component you want
 You are now looking at the Layout Editor context menu*
 Select View callbacks
 Select the callback you wish to create
 The GUIDE will now add it to the m-file and open it.

 There are two key functions:
 set
 sets values
 get
 gets current values

 the get function
 We have seen many examples:
user_data = get(hObject,’String’);
returns string in hObject
user_data = get(hObject,’Value’);
returns value in hObject
user_data = get(hObject,’max’);
returns max possible value in hObject*
same for min
 Please note:
 These commands only work when you are inside the callback
function you are trying to “get” the value of.

 the get function
 In general:
 To access data stored in a component somewhere else in your
program:
user_data = get(handles.component_name,’Value’)
 Where “component_name” is a component which has a property
called ‘Value’
 component_name is generally structured like this:
[component type] [number] i.e. edit1 - pushbutton3 - edit2
 You may change this [But be careful, read the help files]

 the set function
 In general:
 To set [output] values or strings to components in your GUI:
set(handles.component_name,’propertyname’,valuetoset)
 Where “component_name” is a component which has a property
called ‘Value’
 You can set any property like this

 Important:
 You can and most likely will use the following in
conjunction with one another:
set get
num2str str2double
 Example:
set(handles.edittext1,'String',…
num2str(get(handles.slider1,'Value')));
 This will set the “String” for edittext1 as the “Value” of slider1.
The num2str is used because the “String” must be a string and the
“Value” is stored as a number so, num2str converts it accordingly.

 Programming
GUI
 Push Button
 Toggle Button
 Radio Button
 Check Box
 Edit Text
 Slider
 List Box
Components
 Pop-Up Menu
 Panel
 Button Group
 Axes
 ActiveX Control

Programming the GUI
Components
 Push Button
 Push Button
 This example contains only a push button.
Clicking the button, closes the GUI.
 This is the push button's Callback. It displays the string Goodbye at the
command line and then closes the GUI.
function pushbutton1_Callback(hObject, eventdata, handles)
disp(‘Goodbye’)
delete(handles.figure1);

Programming the GUI
Components
 Toggle Button
 The callback for a toggle button needs to query the toggle button to
determine what state it is in. MATLAB sets the Value property equal to
the Max property when the toggle button is pressed (Max is 1 by default)
and equal to the Min property when the toggle button is not pressed
(Min is 0 by default).
 The following code illustrates how to program the callback in the GUI M-
file.
function togglebutton1_Callback(hObject, eventdata, handles)
button_state = get(hObject,'Value');
if button_state == get(hObject,'Max')
% Toggle button is pressed-take approperiate action
% ...
elseif button_state == get(hObject,'Min')
% Toggle button is not pressed-take appropriate action
...
end

Programming the GUI
Components
 Radio Button
 You can determine the current state of a radio button from within its
callback by querying the state of its Value property, as illustrated in the
following example:
if (get(hObject,'Value') == get(hObject,'Max'))
% Radio button is selected-take appropriate action
else
% Radio button is not selected-take appropriate action
end
 Note: You can use a button group to mange exclusive
selection behavior for radio buttons and toggle buttons.

Programming the GUI
Components
 Check Box
 You can determine the current state of a check box from within its
callback by querying the state of its Value property, as illustrated in the
following example:
function checkbox1_Callback(hObject, eventdata, handles)
if (get(hObject,'Value') == get(hObject,'Max'))
% Checkbox is checked-take approriate action
else
% Checkbox is not checked-take approriate action
end

Programming the GUI
Components
 Edit Text
 To obtain the string a user types in an edit box, get the
String property in the the Callback.
function edittext1_Callback(hObject, eventdata, handles)
user_string = get(hObject,'String');
% Proceed with callback
 Retrieving Numeric Data from an Edit Text
Component
 MATLAB returns the value of the edit text String property as a
character string. If you want users to enter numeric values,
you must convert the characters to numbers. You can do this
using the str2double command, which converts strings to
doubles. If the user enters nonnumeric characters, str2double
returns NaN.

Programming the GUI
Components
 Edit Text (cont.)
 You can use the following code in the edit text callback. It gets
the value of the String property and converts it to a double. It
then checks whether the converted value is NaN (isnan),
indicating the user entered a nonnumeric character and displays
an error dialog (errordlg).
function edittext1_Callback(hObject, eventdata, handles)
user_entry = str2double(get(hObject,'string'));
if isnan(user_entry)
errordlg('You must enter a numeric value', ...
'Bad Input','modal')
return
end
% Proceed with callback...

Programming the GUI
Components
 Slider
 You can determine the current value of a slider from
within its callback by querying its Value property, as
illustrated in the following example:
function slider1_Callback(hObject, eventdata, handles)
slider_value = get(hObject,'Value');
 The Max and Min properties specify the slider's
maximum and minimum values. The slider's range is
Max - Min.

Programming the GUI
Components
 List Box
 When the list box Callback is triggered, the list box Value property
contains the index of the selected item, where 1 corresponds to the first
item in the list. The String property contains the list as a cell array of
strings.
 This example retrieves the selected string. It assumes listbox1 is the
value of the Tag property. Note that it is necessary to convert the value
returned from the String property from a cell array to a string.
function listbox1_Callback(hObject, eventdata, handles)
index_selected = get(hObject,'Value');
list = get(hObject,'String');
item_selected = list{index_selected};
% Convert from cell array to string

Programming the GUI
Components
 Pop-Up Menu
 When the pop-up menu Callback is triggered, the pop-up menu Value
property contains the index of the selected item, where 1 corresponds to
the first item on the menu. The String property contains the menu items
as a cell array of strings.
 Using Only the Index of the Selected Menu Item
 This example retrieves only the index of the item selected. It uses a
switch statement to take action based on the value. If the contents of the
pop-up menu are fixed, then you can use this approach. Else, you can
use the index to retrieve the actual string for the selected item.
function popupmenu1_Callback(hObject, eventdata, handles)
val = get(hObject,'Value');
switch val
case 1
% User selected the first item
case 2
% User selected the second item
end

Programming the GUI
Components
 Panel
 Panels group GUI components and can make a GUI easier to
understand by visually grouping related controls. A panel can contain
panels and button groups as well as axes and user interface controls
such as push buttons, sliders, pop-up menus, etc. The position of each
component within a panel is interpreted relative to the lower-left corner
of the panel.
 Generally, if the GUI is resized, the panel and its components are also
resized. However, you can control the size and position of the panel and
its components. You can do this by setting the GUI Resize behavior to
Other (Use ResizeFcn) and providing a ResizeFcn callback for the
panel.
 Note: To set Resize behavior for the figure to Other (Use ResizeFcn),
select GUI Options from the Layout Editor Tools menu.

Programming the GUI
Components
 Button Group
 Button groups are like panels except that they manage exclusive
selection behavior for radio buttons and toggle buttons. If a button group
contains a set of radio buttons, toggle buttons, or both, the button group
allows only one of them to be selected. When a user clicks a button, that
button is selected and all others are deselected.
 The following figure shows a button group with two radio buttons and two
toggle buttons. Radio Button 1 is selected.

Programming the GUI
Components
 Button Group (cont.)
 If a user clicks the other radio button or one of the toggle buttons, it becomes
selected and Radio Button 1 is deselected. The following figure shows the
result of clicking Toggle Button 2.
 The button group's SelectionChangeFcn callback is called whenever a
selection is made. Its hObject input argument contains the handle of the
selected radio button or toggle button.

Programming the GUI
Components
 If you have a button group that contains a set of radio buttons
and toggle buttons and you want:
 An immediate action to occur when a radio button or toggle button is selected,
you must include the code to control the radio and toggle buttons in the button
group's SelectionChangeFcn callback function, not in the individual toggle
button Callback functions. Color Palette provides a practical example of a
SelectionChangeFcn callback.
 Another component such as a push button to base its action on the selection,
then that component's Callback callback can get the handle of the selected
radio button or toggle button from the button group's SelectedObject property.
 This example of a SelectionChangeFcn callback uses the Tag
property of the selected object to choose the appropriate code to
execute. Unlike other callbacks, the hObject argument of the
SelectionChangeFcn callback contains the handle of the
selected radio button or toggle button.

Programming the GUI
Components
 Example:
function uibuttongroup1_SelectionChangeFcn(hObject,eventdata,handles)
switch get(hObject,'Tag') % Get Tag of selected object
case 'radiobutton1'
% Code for when radiobutton1 is selected.
case 'radiobutton2'
% Code for when radiobutton2 is selected.
case 'togglebutton1'
% Code for when togglebutton1 is selected.
case 'togglebutton2'
% Code for when togglebutton2 is selected.
% Continue with more cases as necessary.
otherwise
% Code for when there is no match.
end

Programming the GUI
Components
 Axes
 Axes

Programming the GUI
Components
 ActiveX Control
 ActiveX

Programming for the GUI
 Tips:
 Set the initial values for everything
 Deal with invalid inputs (many different ways to do
this)
 Run most of your code from a pushbutton, rather than
small steps as soon as they enter some data. [Unless
carefully designed, then the opposite may work better]
 Use the property inspector!
 Be creative!
 Explore!

Creating a MATLAB GUI –
Summary
 Creating GUI’s in MATLAB
 Use the GUIDE to create what you see
 It will then create the basic m-file
 Program the m-file
 Utilize the callbacks of the components
 The set, get, num2str, str2num functions are good
 Read more about specific details you want to
know more about

Further Understanding
 If you really want to understand the GUI please
refer to:
MATLAB Programming for Engineers – Stephen J. Chapman
 Ch 5 “User-Defined Functions”
 7.3 “Structure Arrays”
 7.4 “Function Handles”
 Ch 9 “Handle Graphics” **
 Ch 10 “Graphical User Interface” **
 MATLAB Help files on:
 About GUIs in MATLAB
 Creating Graphical User Interface **
** denotes highest level of
importance

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